This invention relates to testing apparatus such as ultrasonic flaw detectors having both analog and digital signals present in various parts thereof and, more particularly, to such apparatus in which noise present in the digital portion of the apparatus is prevented from corrupting the analog signals and thereby invalidating a test involving the apparatus.
Ultrasonic testers for the non-destructive testing of objects are well known in the art. In operation, ultrasonic waves are generated by appropriate transducers and directed at an object under test Depending upon the test being performed, the wave may pass through the object, or strike its surface and be reflected back. The resultant return wave is converted to an analog signal whose characteristics (amplitude, for example) are indicative of the structure of the object. There are various applications for testing apparatus such as ultrasonic wave testers. Representative test applications are shown in U.S. Pat. Nos. 4,821,575, 4,437,332, 4,432,235, 4,373,394, 4,333,346,4,289,033, 4,169,662, 4,129,041, and 4,102,205, all of Which are assigned to the same assignee as the present application.
As indicated in various of these patents, microprocessors are used with the testing apparatus. More recently, personal computers (PC's) have also been employed with the apparatus. A particular advantage with using PC's is that they are easily programmed to allow a wide range of post testing data analysis. For this purpose, the return information is converted to digital data which are stored for later retrieval and analysis. Prior to the start of a test, digital information is sent over the bus to configure the test apparatus for a chosen set of test parameters. The digital data is routed over a digital bus to a storage site. As is typical, the frequency of digital information transmitted over the bus is in the range of 5 Mhz-10 Mhz. These frequencies, however, correspond to those of the ultrasonic transducers within the apparatus. Digital noise which is present on the bus is picked up by amplifiers within the ultrasonic portion of the apparatus. Because of the overlapping frequencies, the amplified digital noise is integrated with the ultrasonic signals, thus distorting this latter signal and the information it contains about the object. The resultant distortion can, effectively, invalidate the test. It is therefore important, not only for ultrasonic wave testing, but also for similar test configurations where analog and digital signals are present, to prevent the noise present on the digital side of the apparatus from adversely effecting the analog signals.